It is commonly assumed that the length of the antenna to be resonant at the connection to the antenna feed line should be only reactive component of the resistance. This condition can soften or simply ignored if used simple wire antenna (in the form of a long wire ) . A simple wire antenna can be seen as a modernized antenna "L -type " , but there are differences - the length of a wire antenna can be chosen arbitrary , as well as the need for a grounding system . Wire antenna with an arbitrary length can handle the entire range of the HF bands, some bands antenna will have repercussions in the other will have to reckon with the reactive component of the input impedance . If a wire antenna to connect a coaxial cable , you must use a transformer resistance , to take measures to compensate for the reactance . Diagram of a complex shape and is close to the antenna radiation pattern of harmonic in some areas will have an asymmetrical shape. To work in a multi-band wire antenna should have a matching device . And to improve the characteristics of the antenna wire requires the use of special earthing system (Figure) . The length of wire grounding wire antenna must comply with the wavelength at which the antenna is working , it is advisable to use two wires. One wire should pass under the antenna and the other at the other end . The wires may be arranged on the surface or buried to a depth of 20 centimeters. To match the wire antenna with a coaxial cable can be used for matching devices shown in the figures below. If the input impedance of the antenna wire is less than or equal to the resistance of the cable you need to use the first pattern matching device if more then a second picture of the matching device. In the second picture below 4:1 transformer used .
Saturday, August 31, 2013
Saturday, August 17, 2013
For balancing and harmonizing Ham antennas can be used aperiodic ferrite baluns. These devices can operate in the Amateur Radio HF and VHF bands. These aperiodic balun on their wires occur with the same high-frequency currents in the opposite direction, resulting in a ferrite core simmeriruyuschego devices resulting magnetic field is zero. If the load (antenna) that there is an asymmetry in the ferrite appears not compensated magnetic flux. Depending on the size of the ferrite core and the wire cross-section aperiodic balun can be used on the transmitter power is a few milliwatts to several kilowatts. To match the antenna can be used by various schemes aperiodic ferrite baluns. The following figures show these schemes.
This figure shows a diagram of a balun with crown windings, it does not produce the transformation of input and output impedance. One of the windings is needed to improve the characteristics of the ferrite balun in the range of 28 MHz amateur radio. The two windings are wound bifilar and one separately.
For balancing and alignment of antennas with a high input impedance can be used a second-figure, in this scheme, the transformation of the input and output resistance by a factor of 1:4. In order to be symmetry was in all the bands to perform the winding so that would be between the wires was a small and constant distance along the winding. This scheme provides a good agreement with a coaxial cable with an impedance of 50 ohms ... 75.
For balancing and alignment of antennas with low resistance can apply an apparatus as shown in the figure. The input impedance of the antenna may be approximately 20 ohms. The transformation ratio 4:1 zeal.
To change the transformation ratio of the ferrite aperiodic balun can apply this scheme. The transformation ratio can be varied from 1:4 to 1:10
If you need to agree on an asymmetrical antenna and asymmetric power line that is now such a scheme, with a ratio of 4:1.
This scheme is applied on a ferrite ring if necessary to carry out a phase shift of 180 degrees in an unbalanced line.
Ferrite matching devices do not make a large attenuation in the antenna gain and is resistant to momentary overloads.
Posted by karan at 2:35 AM
Saturday, August 10, 2013
To match the output stage of the transmitter antenna to the power line, you can use proprietary matching devices for example mfj. But if you do not have or can not buy it, then you can build a device to align antennas shown in the figure. This is a matching device used to adapt the output of the transmitter with a resistance of 50 ohms with balanced and unbalanced power line connected to the antenna input impedance from 10 to 4000 ohms. Between the transmitter output and the input matching device placed SWR. After SWR transmitter signal applied to the input matching circuit devices for L1-C1 (L1A-C1, L1B-C1) which has inductive coupling with the antenna circuit. Setting the Loop L1-C1 made pripomoschi capacitor C1. Setting the antenna circuit L2-C2 (L2AB-C2C3) made capacitors C2 and C3. By the antenna circuit may be connected balanced or unbalanced load. The adjustment is made independent of each other capacitors C2 and C3. Switch matching device has four sections at five positions (or more depending on the number of bands). Coils L1A and L1B has four turns in the range of 80 and 40 meters, both coils are connected in series (8 turns), other bands parallel. Parallel connection improves the agreement with the 50 ohm output of the transmitter. All coils are wound on a device matching the same frame having a diameter of 75 mm. Coils L2A and L2B are approximately 28-30 turns. Since capacitors matching device are under a lot of stress, they must be isolated from each other and from the metal housing of the device, the handle on the axes of the capacitors should also be insulated. The second figure shows the performance of the matching coil unit.
Posted by karan at 8:28 AM
Sunday, August 4, 2013
The first figure shows a conventional antenna Delta with dimensions for a range of 40 meters. The size of the delta can be calculated by the formula L = 304 / F: L - perimeter of the delta, F - frequency at which it is set. At the point of connection of the coaxial cable included tuning loop length of 80 centimeters. Setting the delta is produced by this train on a minimum SWR. The antenna radiates perpendicularly to the antenna plane. Increase the gain of the delta can be placed at a distance L / 4 from the existing framework of another of the same frame of the same length. Delta gain increases due to the fact that one performs the role of the delta frame vibrator and the other reflector (second figure), i.e. the antenna is unidirectional. In order to change the direction of emission of the delta to the framework necessary to connect an additional antenna loop length L / 4 from the same coaxial cable, and set the switch (third picture). Cable length of frames to loop can be arbitrary. This antenna system can operate only on one range. Strengthening the double delta of about 7 dB. For a more exact matching antenna tuner is needed.
The distance between the borders of the delta in meters:
28 MHz - 2.65
21 MHz - 3.54
14 MHz - 5.32
7 MHz - 10.64
3.6 MHz - 20.2
Loop length in meters:
28 MHz - 1.75
21 MHz - 2.34
14 MHz - 3.52
7 MHz - 7.02
3.6 MHz - 13.33
(Dimensions loop length for the cable impedance of 75 ohms for the other cables needed and stored in the velocity factor.)
Posted by karan at 8:12 PM